The trucking industry has for many years used tractor/trailer combinations to transport cargo over the roadways to intended destinations. As shown in FIG. 1, tractor 10 and trailer 20 are mechanically coupled together so that the tractor can pull the trailer with its cargo in an efficient and cost effective manner. Various links between the tractor and the trailer provide vehicle subsystems with power and/or control signals to operate. Hydraulic, pneumatic, electrical and other subsystems on the tractor/trailer combination have associated electrical conductors and pneumatic lines running therebetween so these subsystems can operate. With respect to electrical subsystems, a tractor/trailer combination typically includes a tractor 10 and trailer 20 and a power bus 30 electrically connected to one or more batteries 32, which are typically charged by an alternator 34 mechanically driven by a tractor engine 15. Thus, electrical power is distributed from tractor 10 to subsystems in trailer 20.
The trucking industry has historically lagged behind other industries with respect to technological innovation, but recently has been incorporating more and more sophisticated electronic subsystems in both tractors and trailers. For example, regulatory changes arising from safety concerns have led to the incorporation of trailer antilock braking systems (ABS), frequently microprocessor-controlled, in trailers in order to minimize the risk of trailer skids and jackknifing. New trailers are being constructed with ABS, while older trailers are being retrofitted to incorporate ABS. These systems may include, for example, actuators and transducers operatively connected to the trailer wheels and braking hardware, controlled by electronic circuits located elsewhere on the trailer and tractor. As shown in FIG. 1, an antilock braking system 100, as well as other subsystems, conventionally receives electrical power from power bus 30.
Antilock braking systems may produce data signals which indicate various conditions of the ABS. These data signals may include, for example, a failure warning signal which is asserted if an ABS microprocessor detects a failure within itself or other components of the ABS. In some applications, a data signal may drive a light-emitting diode (LED) or other indicator. Conventionally, the tractor/trailer operator has no external indication of the state of the ABS. Even those systems having an external indicator may not allow a tractor/trailer operator to inspect the state of the ABS while positioned in the tractor cab with the tractor/trailer combination in operation. The operator typically may have to park the vehicle, exit the cab, and inspect an ABS indicator on the trailer, if present, in order to monitor the state of the ABS. Thus, it may be difficult for the operator to monitor the state of the ABS system while the vehicle is moving.
It may be possible to wire data signals from an ABS to a tractor using a dedicated signal path such as a twisted wire pair passed from the trailer to the tractor. A seven-pin connector has been widely used by the trucking industry to convey electrical power for lighting and equipment operation between a tractor and a trailer. As shown in FIG. 2, the connector 40 includes two disengageable connector portions 50 and 60 to permit the tractor and trailer combination to be disconnected. An example of such a seven-pin connector is illustrated in U.S. Pat. No. 4,969,839 to Nilsson, the entire disclosure of which is specifically incorporated herein by reference. These seven-pin connectors are well known and have been specified by the Society of Automotive Engineering (SAE) according to the standard number "SAE J560", the teachings of which are also incorporated herein by reference.
Each of the sockets 54 in the standard seven-pin connector (SAE J560) is an electrical conductor carried by the plug portion 50 of the connector and which is adapted to mate with a corresponding electrical pin 63, also an electrical conductor, in the receptacle portion 60 of the connector to thereby provide an electrical signal between the tractor and the trailer. The pins and corresponding sockets generally are assigned to specific electrical subsystems, for example, power, ground, turn signals, brake lights, clearance lamps, emergency flashers, and other devices requiring electrical signals.
Until recently, the seventh pin on the connector has been an "auxiliary" pin which could be used for specific electrical purposes or applications on individual tractor/trailer combinations. Pursuant to Federal Motor Vehicle Safety Standard No. 121, however, the National Highway Traffic Safety Administration has mandated that the antilock braking systems of all trailers on the road after Mar. 1, 1998 must not only be powered by the power line that drives the brake lights, but also by a second power line that is connected to the tractor by means of the seventh pin, i.e., the former auxiliary pin. As a result, all seven pins of the connector will soon be dedicated to a particular purpose.
Although pins and sockets of the seven-pin connector may be used to convey an ABS status signal to a tractor, the generally limited circuit capacity afforded by the standardized connector would be reduced even further. The standard seven-pin connector simply may not provide the circuit capacity needed to convey to a tractor an increased number of data signals from various systems located on trailers, including additional ABS systems which may be present when a tractor is connected to multiple trailers. Connectors with greater capacity could be employed, but the seven-pin connector (SAE J560) is an industry standard for tractor/trailers. Alternative communications techniques such as fiber optic links or radio communication through free space may bypass the bottleneck of limited channel capacity in the standard connectors used to connect tractors and trailers, but may require the installation of complex and expensive electronic components. These components, often referred to as "black boxes," may be vulnerable to theft and vandalism when placed on trailers which often are under the control of multiple operators and left in unsecured areas.